Switch



March 1958 R. G. LARSON ETAL 2,826,718

SWITCH Filed Nov. 12. 1953 I a II 25 I T0 SOURCE OF MAINTAINING VOLTAGE 77! I /I\ I I '1 y I l6 2 l 5 ANTENNA '7Tl/ U M +SOURCEOF 27 Y PULSES TRANSMITTER '0 FROM SOURCE OF MAINTAINING VOLTAGE FIG. I

SOURCE OF MAINTAINING SOURCE OF 64 PULSES ANTENNA 7 INVENTORS ROGER G. LARSON EDWARD R. MITTELMI IN F I G 2 PETER II. WALSH ATTORNEYS to Fig. l, the reference numeral United States Patent G SWITCH Application November 12, 1953, Serial No. 391,778 7 Claims. (Cl. 315-39) Rodger G. Larson,

This invention relates to switches and more particularly to switches for controlling the flow of high frequency radio energy.

In many applications of high frequency radio energy such as in radio echo scanning, it is necessary to transmit radio frequency energy pulses of high power sequentially to individual antennae of a group. This requires switch means which can control the flow of large amounts of power and can also transmit low power reflected pulses without appreciable attenuation. The switch means must also disconnect from the transmitter all antennae but the one to be used. Heretofore, gas filled tubes were inserted in the transmission lines for this purpose, but these gas tubes have been found to spontaneously breakdown when traversed by high power radio frequency energy, and switch when switching was not desired. When the gas tubes are modified to prevent such spontaneous breakdowns, such as by increasing the pressure of the gas, the weak reflected signals from the targets are attenuated excessively.

It is an object of this invention to provide new switch means for controlling the flow of radio frequency energy flowing through waveguides and coaxial transmission lines.

A further object of this invention is to provide switch means for high frequency radio energy, which switch means are capable of controlling large amounts of power for predetermined periods of time.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein:

Fig. 1 is a sectional view of the switch of this invention as used in a waveguide; and

Fig. 2 is a sectional view of a modification of the switch of this invention as used in a coaxial transmission line.

Referring now to the drawings and more particularly 10 designates a radio frequency transmitter which is connected to a main waveguide 11. A branch waveguide 12a is connected at one end to the main waveguide 11 in the form of a T and at the other end to one end of a special section of waveguide 13 by rings 14. The waveguide section 13 is connected at the other end to one end of a branch waveguide 12 which is connected to an antenna 20 at its other end. A mercury arc tube 15, which is positioned in the section 13, comprises an anode 16 which is affixed to but insulated from a portion of the wall of the waveguide section 13 by insulators 17, a cathode 18 consisting of a pool of mercury located in a depression of the waveguide section 13, and an ionizing electrode 19. The anode 16 and the cathode 18 are located on opposite sides of the waveguide section 13 so that an electron discharge from the cathode 18 to the anode 16 traverses the waveguide section 13. The ionizing electrode 19 is connected to a source of ionizing pulses 27 by a conductor 22 which passes through the wall of the waveguide section 13 and is insulated from the wall by an insulating bushing 23 sealed at both ends to the conductor 22 by seals 24 and also to the wall of the waveguide section 13. The ionizing electrode 19 is disposed close to the surface of the mercury pool 18 to effect a high potential gradient between the pool 18 and the electrode 19 when a voltage is applied across them. Two ceramic windows 21 are sealed across the waveguide section 13 on either side of the anode 16 and the cathode 18 to complete an airtight envelope for the tube 15, which envelope is evacuated. Conductors 25 and 26 connect the anode 16 and the cathode 18 respectively to a source of voltage (not shown) for maintaining a discharge through the tube 15.

In the operation of the described apparatus, the mercury arc tube 15 does notmaterially interfere with the transmission of radio frequency energy from the transmitter 10 to the antenna 20 when there is no electron discharge from the cathode 18 to the anode 16. When the flow of energy through the waveguide section 13 is to be interrupted, a voltage from the source 27 is applied across the electrode 19 and the cathode 18. The steep potential gradient established by this voltage causes the mercury in the space between the cathode 18 and the electrode 19 to are. The direct voltage applied across the anode 16 and the cathode 18 maintains the discharge. After a discharge across the tube 15 has been established, the ionizing voltage from the source 27 is removed.

The stream of mercury ions in the tube 15 during conduction, acts as a low impedance path across the waveguide section 13, effectively short-circuiting the wave guide 13 and preventing the flow of energy to the antenna 29. Any reflected pulses received by the antenna 29 while the tube 15 is conducting are also short-circuited by the discharge. The discharge may be maintained for as long an interval as desired by the direct voltage applied across the anode 16 and the cathode 18, but when transmission to the antenna 20 is to be resumed, the direct voltage applied across the tube 15 is interrupted and the discharge ceases, deionization of the mercury being almost instantaneous.

The initiation of a discharge in a mercury arc tube is generally difiicult, the normal method being the withdrawal of a conducting electrode from the mercury or of the mercury from an electrode. However, by positioning the ionizing electrode 19 close to the pool of mercury 18, a high potential gradient sufficient to cause arcing is established between the two electrodes when a voltage from the source 27 is applied across them. Because it is difficult to establish an arc in the tube 15, high power radio frequency pulses passing through the waveguide section 13 will not produce a discharge and cause switching when switching is not desired. The pool of mercury serves as a reservoir of ions and for this reason the tube 15 is capable of handling high current density fiows and high power. If the tube 15 is spaced approximately an odd number of quarter wavelengths, at the operating frequency of the system, from the junction of the main waveguide 11 and the branch waveguide 12a, a discharge through the tube 15 will produce the effect of a very high impedance at the junction of the waveguides 11 and 12a, and little radio frequency energy will flow from the waveguide 11 into the waveguide 12a. A spacing of the tube 15 from the junction of the waveguides 11 and 12a of one quarter wavelength is preferred.

In the modification of Fig. 2, the switch is shown connected in a coaxial transmission line (hereinafter referred to as coax). A transmitter 46 is connected to a main coax 48 which comprises an outer conductor 51 and an inner conductor 52. A branch coax 49 comprising an outer conductor 53 and an inner conductor 54 is connected to the con)? 48 in the form of a T and serves to conduct energy from the transmitter 46 to an antenna 47. A mercury arc tube 55 which comprises an evacuated airtight envelope 56, formed of electrically insulating material such as glass, and containing an anode 57 a mercury pool cathode 58 and an i'oniiing electrode 59 is mounted within the outer conductor 53 in' series with the inner conductor 54 of the branch coax 49. The ionizing electrode 59 is connected by a conductor 61 to a source of ionizing pulses 64. The conductor 61, where it passes through the envelope 56 and the outer conductor 53, is surrounded by' an insulating sleeve 62 which has a hermetic seal 63 at each end. The inner conductor 54 r is interrupted at the tube 55, forming two parts 54a and 54b. The anode 57 is connected to one part 54a at the end which is adjacent the other part 54b, and the cathode 58 is connected to the other part 54b at the end which is adjacent the anode 57. The space between the anode 57 and the cathode 58 serves" as a break the circuit from the transmitter 46 to the antenna 47. A source of direct voltage 65 is connected across the anode 57 and the cathode 58 to maintain a discharge through the tube 55.

In operation, the tube 55 serves as a switch in series with the two parts 54:: and 54b of the inner conductor 54. No conduction can take place through the inner condoctor 54 when there is no discharge through the tube 55. To close the circuit from the transmitter 46 to the antenna 47, a voltage from the source 64 is applied across the electrode 59 and the cathode 58 producing an arc between the two, and the voltage from the source 65 is applied across the anode 57 and the cathode 58 to establish' conduction through the tube 55. The ion stream within the tube 55 serves as a conductive connection between the two parts 54a and 54b of the inner conductor 54, and the coax 49 can conduct energy in either direction. The direct voltage from the source 65 can be maintained for as long as conduction through the coax 49 is desired, but when the transmission of radio frequency energy to the antenna 47 is to be interrupted, the direct voltage from the source 65 is interrupted and the discharge through the tube 55 ceases, opening the circuit.

The switch of this invention provides a means for controlling the conduction of high frequency radio energy through high frequency transmission lines, elfectively cutting-oh the flow of high power radio frequency pulses when desired, and also providing a low resistance path for the desired transmission of low power pulses. This switch is capable of high current density discharges because the mercury pool cathode serves as a reservoir for large quantities of mercury ions. of this invention is positive and the time of initiation of conduction and the period of conduction are both readily controlled without the danger of spontaneous breakdowns.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A switch device for radio frequency energy comprising a hollow conductor adapted to conduct radio frequency energy, an electron tube mounted in said hollow conductor in the path of radio energy flow, said electron tube comprising anenve'lope containing an anode, a cathode of mercury and an ionizing electrode, means for connecting a first voltage across said ionizing electrode and said cathode, and means for connecting a seconddirect voltage across said anode and said cathode.

2. The switch device defined in claim 1 in which said Switching by the device hollow conductor comprises a branch waveguide, said electron tube being positioned transverse of said wave guide with said anode adjacent one wall of said waveguide and said cathode adjacent an opposite wall of said waveguide.

3. The switching device defined in claim 1 in which said hollow conductor comprises the outer conductor of a coaxial transmission line, said transmission line having also an inner conductor comprising two spaced apart wires which are coaxial with said outer conductor, said electron tube being connected between said wires with said anode connected to one said wire and said cathode connected to the other said wire.

4. A radio frequency switch comprising a waveguide, a first portion of a wall of said waveguide being insulated from the rest of said waveguide, a second portion of a wall of said waveguide having a depression therein positioned opposite said first portion and adapted to contain mercury, rneans for connecting a direct voltage between said insulated portion of said waveguide and said depression, an auxiliary electrode insulated from said wave guide and located adjacent said depression, and means for connecting a voltage between said auxiliary electrode and said depression.

5. A radio frequency switch comprising a coaxial transmission line having an outer hollow conductor and an inner conductor; said inner conductor including a hermetically sealed envelope; said envelope containing an anode, a depression opposite said anode and adapted to contain mercury, tioned adjacent said depression; said inner conductor further including a first wire coaxial with and insulated from said outer conductor and having one end connected to said depression; means for connecting a direct voltage across said anode and said depression; and means for connecting a voltage across said auxiliary electrode and said depression.

6. A switch device for'selectively controlling the open and closed conditions of the circuit through a hollow me other of said circuit conditions, said cathode being a pool of mercury, 21 separately energized make-alive electrode for initiating a discharge between the cathode and anode, and means for applying a discharge rnaintaining direct current voltage across the cathode and anode.

7. A switching device for controlling the flow of high power radio frequency energy along a hollow conductor, comprising a hollow conductor, a mercury arc tube mounted in said conductor and having an anode, a mercury cathode, and an ionizing electrode, means for connecting a discharge-maintaining potential across the anode and said cathode, means for applying a discharge initiating potential between the ionizing electrode and said cathode, and means coupling the discharge path of the anode and said cathode in energy-flow controlling relation to said conductor.

References Cited in the file of this patent UNITED STATES PATENTS and an auxiliary electrode posi- 

